definition
strict definition
irregular roof
An uncommon roof form that does not approximate another defined type, beyond small deviations from those types.
An irregular roof type is one which does not approximate any other defined roof type. Roofs which deviate from defined types to a small degree can generally be included in those types, so the irregular category is reserved for especially uncommon forms.
Small departures from a regular type generally remain within that type. A slight asymmetry alone need not make a roof irregular.
A combination of roof parts can still approximate a defined form. The irregular category is reserved for the uncommon forms that cannot reasonably be described that way.